The use of polysiloxanes in coating compositions, including both aqueous emulsions and solutions, is well known. Such coating compositions are particularly desirable where the coated article will be subjected to elevated temperatures, since many polysiloxanes are more resistant to thermal degradation than are most polymers having carbon atoms in their backbone.
For many applications it is desirable that the coating composition be cured by a suitable cross-linking reaction after application to the substrate. For polysiloxanes this can be accomplished by the reaction of at least two silanol groups on the polysiloxane with at least two hydroxyl or alkoxy groups linked to a silicon atom of a silane cross-linking agent having at least two such reactive functional groups per molecule thereof.
These curing reactions are known to be catalyzed by certain organo metallic compounds, such as alkyltin salts of fatty acids. Where such active catalysts have hitherto been employed in such coating compositions, the stability of the liquid coating composition has been seriously compromised by premature gelation. This has sometimes been overcome by substituting less active organozinc compounds for the more highly active organotin catalysts, thereby extending the pot life of the liquid coating composition, but at the cost of requiring higher temperatures and/or longer times to effect satisfactory cure of the coating on the substrate.